Comprehensive Comparison of Position Correction Information: Differences Between Network RTK and Satellite-based CLAS/MADOCA and an LRTK Implementation Guide

Table of Contents

• What is position correction information? Its necessity and meaning in RTK surveying

• Mechanism, advantages, and limitations of network RTK

• Mechanism, advantages, and limitations of satellite correction (CLAS / MADOCA)

• Comparison of network RTK and satellite correction methods (accuracy, latency, stability)

• Criteria for choosing the right method by region, application, and communication environment

• Practical use-case differentiation (civil engineering surveying, structural construction, mountainous areas, disaster sites)

• Effect of introducing simplified RTK surveying supporting both methods with LRTK

• FAQ

What is position correction information? Its necessity and meaning in RTK surveying

Position correction information, essential for high-precision surveying, refers to data used to correct GNSS (Global Navigation Satellite System, e.g., GPS) positioning errors. Standalone GNSS positioning typically incurs errors of several to a dozen meters due to satellite orbit and clock errors, ionospheric and tropospheric delays, and other factors. While a few meters of error is acceptable for everyday car navigation or smartphone maps, in civil engineering surveying and construction sites even errors of a few centimeters can be unacceptable. To cancel positioning errors, high-precision positioning techniques such as RTK use correction data from reference stations or satellite-based error corrections to increase accuracy. This correction data is what we call "position correction information," and applying it in real time can improve GNSS positioning accuracy to the centimeter level.

In RTK surveying (Real Time Kinematic positioning), two GNSS receivers are prepared: a reference station with known coordinates and a rover that observes while moving. The reference station calculates the difference between its measured position and the true position and sends that difference as correction information to the rover via communication. The rover applies that correction to its own observations in real time, which cancels atmospheric and satellite errors and enables centimeter-level accuracy. Thus, position correction information is the core of RTK surveying; only by properly obtaining and using correction information can high-precision GNSS positioning be realized in the field.

Mechanism, advantages, and limitations of network RTK

"Network RTK" (communication-based RTK) refers broadly to methods that achieve centimeter-level positioning by communicating correction information from reference stations to rovers in real time. Typical examples are local RTK, where a reference station is set up near the site and correction data is sent by radio (e.g., UHF) to the rover, and network RTK using data distributed via the Internet from a network of reference stations (e.g., VRS methods). Both share the fundamental principle of delivering correction information from ground reference stations to the rover by communication.

The greatest advantage of communication-based RTK is its extremely high accuracy and immediacy. Real-time relative positioning can remove most GNSS error sources, so under good conditions one can achieve astonishing accuracy of about ±1–2 cm horizontally and ±3–4 cm vertically. Initialization time until a fixed solution (convergence from float) is short—typically a few seconds to about 30 seconds—and once a fixed solution is obtained, the rover can continuously receive high-precision positions in real time. This makes network RTK suitable for tasks that require immediate high-precision coordinates on site, such as machine guidance and setting out. Local RTK benefits from close proximity between the reference point and survey points, making it easier to maintain consistency with the reference coordinates, while network RTK can ensure stable accuracy over a wide area by using virtual reference station data derived from widely distributed continuous reference stations (e.g., GEONET by the Geospatial Information Authority).

However, communication-based RTK has several constraints. First is the reliance on communication environment. For radio systems, the effective range is limited to where the reference station's signal reaches (typically a few kilometers), and terrain or distance can be problematic. For network RTK, mobile phone or Internet connectivity is required; in tunnels or mountainous areas where there is no coverage, correction data cannot be received. If communication is interrupted, positioning accuracy immediately degrades, and if corrections are unavailable for a long time the fixed solution cannot be maintained. Second, a reference station must be provided. If you set up your own reference station, tripod, antenna, and radio equipment must be prepared and set up, which is laborious, and fixed high-precision receivers are expensive. Using a network service also often requires subscription or administrative contracts, incurring monthly fees in some cases (e.g., joining a VRS distribution service). Also, RTK using a single reference station degrades in correction accuracy as the baseline length (distance from the reference station) increases, making it unsuitable for very wide-area positioning spanning tens of kilometers without switching reference stations. Thus, communication-based RTK offers high accuracy and immediacy but with significant dependence on communication infrastructure and reference stations.

Mechanism, advantages, and limitations of satellite correction (CLAS / MADOCA)

Satellite correction methods improve positioning accuracy using augmentation signals from artificial satellites rather than relying on ground communications. Representative services are CLAS (Centimeter Level Augmentation Service), a centimeter-level positioning augmentation service provided by Japan’s Quasi-Zenith Satellite System (QZSS, "Michibiki"), and MADOCA-PPP (Multi-GNSS Advanced Orbit and Clock Augmentation), a wide-area PPP-style augmentation using QZSS. These services are characterized by broadcasting correction information from the positioning satellites themselves; if a receiver can receive the corresponding signals, correction information can be used without ground reference stations or ground communication lines.

CLAS is a PPP-RTK style augmentation service for Japan, sending SSR (State Space Representation) format correction information—modeling satellite orbit and clock errors and ionospheric and tropospheric delays—based on observation data collected from the Geospatial Information Authority’s continuous reference station network (about 1,300 stations). The corrections are broadcast nationwide via QZSS L6-band signals (L6D/QZS-L6), so compatible receivers can achieve centimeter-level positioning directly from satellites even in mountainous areas without mobile coverage. Since users do not need to set up their own reference stations, CLAS offers the advantage of generally uniform accuracy across Japan. Positioning using CLAS, often called PPP-RTK, requires about one minute of initial convergence, but once stable can reach approximately 5–7 cm accuracy (RMS) horizontally. Although slightly less accurate than local RTK, CLAS’s simplicity without special communication infrastructure has led to wide use in surveying, agricultural machinery, and drone positioning across Japan.

MADOCA-PPP is another satellite augmentation service using QZSS, designed as a wide-area PPP method covering the Asia–Oceania region. It estimates satellite orbit and clock errors from data collected by global and regional reference station networks (e.g., IGS and MIRAI) and broadcasts those corrections via QZSS L6-band signals (L6E). Like CLAS, it can be used without local reference stations, but as a PPP method it requires longer initial convergence—about 20–30 minutes in some cases—and stable accuracy is lower, around 10 cm horizontally (and possibly worse under some conditions) compared to RTK or CLAS. Its advantage is wide coverage, making it usable overseas and at sea where terrestrial communication infrastructure is unavailable. For example, MADOCA is useful for ship navigation and surveying on remote islands. Besides correction value utility, precise clock and orbit information from satellites can also improve meteorological predictions (e.g., estimating observed precipitable water) and have applications in time synchronization technologies. MADOCA entered full operational service in 2024 and, at present, prioritizes wide-area coverage over immediate responsiveness for real-time positioning.

The greatest benefit of satellite correction is its convenience of wide-area availability without reliance on ground infrastructure. With a CLAS-capable receiver, centimeter-level positioning is available anywhere in Japan (given clear sky visibility) at no additional cost. In mountainous or disaster-struck areas where communication networks are down, as long as QZSS signals reach, high-precision GNSS positioning is possible. Because correction information is broadcast from the national satellite system, it is provided free of charge, meaning there are no monthly running costs. Another advantage is scalability: performance does not degrade if many users use the service simultaneously, since corrections are broadcast to all receivers at once and are not subject to access congestion.

However, satellite correction also has caveats. First, compatible receivers are required: a high-precision GNSS receiver and antenna capable of receiving QZSS L6 signals are necessary; conventional L1/L2-only devices or general positioning modules cannot receive CLAS/MADOCA. Second, initialization takes time: as noted, CLAS requires tens of seconds to about a minute, and MADOCA may take up to about 30 minutes to reach centimeter-level accuracy. This makes satellite methods less suitable for tasks requiring immediate high-precision positioning. Also, positioning accuracy itself is somewhat inferior to RTK: CLAS and MADOCA typically achieve horizontal accuracy within about 10 cm, which is larger than the few-centimeter accuracy of RTK. Vertical accuracy in particular is prone to degradation in satellite augmentation methods, making strict height measurements less suitable. Because the method relies on receiving correction signals from satellites, reception conditions greatly affect performance: while open-sky environments are fine, forests and urban canyons can block L6 signals and interrupt corrections. Correction update intervals are also less frequent than RTK’s sub-second updates (ranging from several seconds to several tens of seconds), so responsiveness to sudden error changes is inferior to real-time RTK. In summary, satellite correction is a method that does not require terrestrial infrastructure and can be used anywhere, but it “depends on environment and application.”

Comparison of network RTK and satellite correction methods (accuracy, latency, stability)

Based on the above, let us compare the main differences between network RTK and satellite correction (CLAS/MADOCA) in terms of accuracy (positioning error), latency (initial convergence and real-time capability), and stability (ease of continuous use). The following table summarizes the characteristics of both.

The table shows that network RTK, while localized and communication-dependent, has the advantage in accuracy and immediacy. Satellite correction, despite some accuracy degradation and time lag, excels in being usable over wide areas without communication infrastructure. Stability depends on conditions: network RTK provides immediate corrections as long as radio or network connections remain, making it strong for dynamic positioning and quick recovery after short satellite outages (if a sufficient number of fixed satellites are available, reconvergence can be instantaneous). Satellite correction, being free from terrestrial communication, cannot operate well when the augmentation signals themselves are blocked; resuming positioning after an interruption may require longer re-convergence time. Conversely, in open-sky environments for static, continuous observations, satellite correction can maintain centimeter-level accuracy stably. Ultimately, the choice comes down to “prefer accuracy and immediacy” versus “prefer convenience and wide applicability.”

Criteria for choosing the right method by region, application, and communication environment

Which method—network RTK or satellite correction—should be used depends on site conditions and required accuracy. Below are criteria for selecting the most suitable method from the perspectives of regional characteristics, application, and communication environment.

• Communication infrastructure availability: Whether mobile phone or Internet connectivity is available at the site is a major deciding factor. In urban areas or sites with adequate communication infrastructure, network RTK (network-type RTK) allows quick, high-precision positioning. In contrast, in mountainous areas, remote islands, or offshore locations beyond mobile coverage, network RTK is practically unusable, making satellite correction (especially CLAS) the only option. In areas without communication coverage, CLAS/MADOCA is the lifeline that supports high-precision positioning.

• Required accuracy and immediacy: If near-millimeter to very high precision and immediate centimeter-level accuracy right after start-up are required, network RTK is appropriate. For example, precise positioning for structural installation or machine control requires accuracy within ±2 cm and instant response, where RTK is highly beneficial. Conversely, if an accuracy of around 10 cm is acceptable or if it’s acceptable to wait several minutes for initial convergence (e.g., for surveys or monitoring), satellite correction is practically sufficient. If you prioritize wide-area coverage and simplicity over real-time responsiveness, CLAS/MADOCA is an attractive choice.

• Extent of survey area: For surveys confined to a small area within a few kilometers of a reference station, network RTK is fine. But for surveys spanning wide areas (e.g., road surveys over tens of kilometers or mobile measurements), a single base station cannot cover everything and accuracy will degrade; consider satellite correction or nationwide network services. In Japan, CLAS-capable equipment can be used nationwide; for cross-border large-area surveys, MADOCA or other countries’ SBAS/PPP services should be considered.

• Working environment (obstruction conditions): In environments with poor sky visibility—forests or dense urban canyons—GNSS may not function adequately. Both methods struggle there, but in terms of recovery speed from temporary obstructions, network RTK is advantageous. For example, when surveying while moving between trees, CLAS may require repeated re-convergence, whereas RTK can often return quickly to a fixed solution as long as correction data continues to be received. If the sky is nearly completely blocked, both the positioning satellites and augmentation satellites (QZSS) may be lost, making satellite correction difficult to maintain. Thus, one rule of thumb is: satellite-based methods for open-sky locations; communication-based methods where obstructions occur.

• Equipment and cost considerations: Initial acquisition and operational costs also inform decision-making. If your organization already has RTK base stations or network contracts and specialized surveying equipment, continue using network RTK. If you lack such infrastructure but want to introduce high-precision positioning easily, satellite correction is attractive because a CLAS-capable GNSS receiver is all you need. Since satellite augmentation signals are provided free, satellite correction reduces running costs. However, consider the purchase cost of compatible equipment (high-precision GNSS receivers require investment, though CLAS-capable models have become more affordable).

In summary, use network RTK in areas with good communication infrastructure when the highest accuracy is required, and use satellite correction where communication is difficult or when convenience is prioritized. Recently, receivers that support both methods in a single unit have emerged, allowing seamless switching between network and satellite modes according to field conditions.

Practical use-case differentiation (civil engineering surveying, structural construction, mountainous areas, disaster sites)

Below are typical scenes showing how network RTK and satellite correction can be used differently in practical fieldwork.

• Civil engineering surveying (general land development and site surveys): In relatively open sites with limited distance from reference points, network RTK is the mainstay. Setting up a base station at a known point allows high-precision real-time surveying within a few kilometers. With the spread of network RTK services, in suburban areas one person can perform surveys by receiving VRS corrections over mobile networks. For large-area as-built surveys, GNSS surveying by walking with a GNSS device can be more efficient than total stations. However, on large development sites that include some mobile-dead zones, consider combining CLAS-capable devices to switch to satellite correction in coverage gaps.

• Structural construction (precise positioning and construction control): For installing bridges, plants, and other structures where millimeter-level control and immediate position checks are required, the immediacy and high accuracy of network RTK are indispensable. Common practice includes mounting rovers on construction machinery or survey prisms and placing a portable base station on site for real-time machine guidance. Network RTK allows immediate confirmation of blade positions and bolt placements, speeding up quality control. If construction occurs in special environments such as mountain tunnels where base station radio cannot reach, satellite correction (CLAS) can be used to determine machine positions or to transfer coordinates measured outside the tunnel to inside. Generally, structural high-precision construction management equals network RTK, but satellite methods can be used complementarily for flexible field response.

• Mountainous area surveying (infrastructure inspection, forestry, topographic surveys): In remote mountainous areas with no mobile coverage, CLAS-capable GNSS receivers are powerful. For example, for forest road surveys or mountain infrastructure inspections, you can set up a receiver, wait a few minutes, and obtain positions within about 10 cm without deploying a base station. Compared to traditional methods requiring triangulation points on summits, CLAS allows direct acquisition of global coordinates at lower elevations, greatly improving efficiency. However, dense forests may block satellite signals, so in forestry surveys it’s necessary to assess GNSS availability before correction method choice. Practically speaking, network RTK in mountains would require setting up temporary radio base stations each time, so CLAS is often the only realistic option.

• Disaster site use (damage assessment and recovery planning): After a major disaster, rapid measurement of terrain changes and damage extent is needed, but communication infrastructure may be down. Satellite correction is extremely useful in such scenarios. Survey teams entering an affected area can start surveying immediately with a CLAS-capable receiver and tablet without spending time setting up a base station. Recording coordinates of landslides or breached embankments on the spot aids recovery planning. While detailed recovery construction later requires network RTK for precise surveying, CLAS’s ease and no-setup nature are ideal for initial damage mapping. The ability to position as long as satellites are operational, even before communication networks are restored, is invaluable in disaster response.

In practice, it is important to use network and satellite methods wisely according to conditions. Hybrid operations using both methods are becoming realistic; for example, primarily use network RTK on site and switch to CLAS for areas with no communication coverage.

Effect of introducing simplified RTK surveying supporting both methods with LRTK

Finally, we introduce LRTK, a modern solution that supports both network RTK and satellite correction. LRTK is an innovative system combining a smartphone with a compact high-precision GNSS receiver to achieve centimeter-level positioning, and it’s gaining attention as an easy-to-use simplified RTK surveying tool for novices. Traditionally, RTK required expensive stationary equipment and complicated setup; with LRTK, a palm-sized dedicated receiver (LRTK Phone) is attached to a smartphone and an app is launched to start. There is no need for complex base station configuration or radio adjustments on site—centimeter-level position measurements can begin with a single tap.

A key feature of LRTK is that it supports both network RTK and satellite correction. Through the smartphone’s Internet connection, it can receive corrections from various network RTK sources (NTRIP distribution), and the device itself can directly receive CLAS signals from Japan’s Michibiki. In other words, in urban or near-office environments it can use network RTK via the Internet, and in mountainous or communication-free areas it can automatically switch to satellite augmentation—enabling both modes with one device. This adaptability to maintain centimeter-level positioning anywhere is a unique advantage of LRTK. In practice, LRTK receivers support three-frequency, multi-GNSS raw data and can achieve professional-grade positioning comparable to conventional units (horizontal ±1–2 cm, vertical ±3–4 cm). CLAS support allows continuous positioning even where mobile signals are absent, enabling surveys in mountainous terrain with vehicles carrying heavy equipment and solo surveys on remote islands.

Introducing LRTK yields substantial benefits. First, surveying efficiency improves: tasks traditionally requiring two people can be done by one, helping alleviate labor shortages. The small, lightweight equipment is easy to carry, enabling rapid deployment and increasing the number of survey points in rough terrain. Second, costs are reduced: reliance on expensive dedicated equipment or base station network contracts is lessened, making centimeter-level positioning accessible to small businesses. Third, data utilization advances: LRTK integrates smartphone apps and cloud services, enabling immediate sharing and analysis of field-acquired position data, contributing to DX (digital transformation) from surveying through design and construction management.

Especially notable is LRTK’s hybrid support for both methods, which allows the device to automatically select the most suitable correction source without user intervention. On site, LRTK maintains network RTK where available, and automatically switches to CLAS when entering areas with poor communication—providing seamless positioning. As a result, stable high-precision positioning is guaranteed in any environment, dramatically improving surveying and construction productivity and reliability. LRTK, which lets users exploit the best correction method without needing to understand the differences in position correction information, is poised to become a powerful solution for future civil engineering surveying sites.

FAQ

Q: Which is more accurate, RTK methods or satellite augmentation (CLAS)? A: Generally, RTK using a single reference station or network RTK is slightly more accurate than CLAS. Under ideal conditions, communication-based RTK can achieve horizontal errors of about 2–3 cm, while CLAS provides model-based satellite corrections and typically yields about 5–10 cm error on average (vertical accuracy in particular favors RTK). Nonetheless, CLAS is sufficiently accurate for many surveying and agricultural applications. Remember: choose RTK for the highest accuracy, and CLAS to balance ease of use and practical accuracy.

Q: Is there a fee to use CLAS or MADOCA correction information? A: No. CLAS and MADOCA-PPP correction signals are provided by the government and there is no usage fee. If you have a compatible GNSS receiver, you can receive the satellite-broadcast correction information free of charge. However, if you also use communication-based RTK services (network RTK), those may require separate contracts or usage fees. Purchasing CLAS/MADOCA-compatible receivers does incur equipment cost, but that is a hardware expense rather than a service fee. In terms of running costs, CLAS/MADOCA are economical since they do not require communication or service subscriptions.

Q: What specifically differs between CLAS and MADOCA, and how should I choose between them? A: Both are QZSS-based satellite augmentation services, but they differ in coverage and method. CLAS is a Japan-focused centimeter-level augmentation designed to achieve a few centimeters of accuracy after about one minute of convergence, using domestic reference station data—making it effective for domestic real-time applications such as agricultural machinery and surveying. MADOCA-PPP is a precision point positioning (PPP) service targeting Asia–Oceania, requiring about 20 minutes of convergence to reach roughly 10 cm accuracy. MADOCA is intended for wide-area navigation and overseas use where CLAS is unavailable. For domestic work, CLAS is generally preferred for its faster convergence and higher accuracy; for overseas or maritime use where CLAS cannot be received, consider MADOCA. Devices that receive both can automatically switch between them.

Q: Can LRTK really provide centimeter-level positioning even outside communication coverage? A: Yes. LRTK supports CLAS signals from the QZSS, so even where mobile phone coverage is absent, the receiver can directly obtain satellite-based correction information and maintain centimeter-level positioning. For example, in remote mountains where a smartphone has no signal, an LRTK receiver can continue receiving corrections from "Michibiki" satellites to provide high-precision positioning. When returning to coverage, it can automatically switch back to network RTK corrections—so users can maintain optimal high-precision positioning regardless of communication environment. In short, with LRTK you can achieve consistent high-precision positioning independent of communication conditions, greatly expanding the range of surveyable sites and proving invaluable in mountainous and disaster-stricken areas.